blockfetcher: add retry for GET and SEARCH operations

Close #3564

Signed-off-by: Ekaterina Pavlova <ekt@morphbits.io>

pkg/services/blockfetcher/blockfetcher.go

@@ -44,6 +44,18 @@ const (
 	defaultHealthcheckTimeout = 10 * time.Second
 )
 
+// Constants related to retry mechanism.
+const (
+	// maxRetries is the maximum number of retries for a single operation.
+	maxRetries = 5
+	// initialBackoff is the initial backoff duration.
+	initialBackoff = 500 * time.Millisecond
+	// backoffFactor is the factor by which the backoff duration is multiplied.
+	backoffFactor = 2
+	// maxBackoff is the maximum backoff duration.
+	maxBackoff = 20 * time.Second
+)
+
 // Ledger is an interface to Blockchain sufficient for Service.
 type Ledger interface {
 	GetConfig() config.Blockchain
@@ -215,7 +227,9 @@ func (bfs *Service) oidDownloader() {
 	}
 	var force bool
 	if err != nil {
-		bfs.log.Error("NeoFS BlockFetcher service: OID downloading routine failed", zap.Error(err))
+		if !isContextCanceledErr(err) {
+			bfs.log.Error("NeoFS BlockFetcher service: OID downloading routine failed", zap.Error(err))
+		}
 		force = true
 	}
 	// Stop the service since there's nothing to do anymore.
@@ -489,21 +503,64 @@ func (bfs *Service) IsActive() bool {
 	return bfs.isActive.Load()
 }
 
+// retry function with exponential backoff.
+func (bfs *Service) retry(action func() error) error {
+	var (
+		err     error
+		backoff = initialBackoff
+		timer   = time.NewTimer(0)
+	)
+	defer func() {
+		if !timer.Stop() {
+			<-timer.C
+		}
+	}()
+
+	for i := range maxRetries {
+		if err = action(); err == nil {
+			return nil
+		}
+		if i == maxRetries-1 {
+			break
+		}
+		timer.Reset(backoff)
+
+		select {
+		case <-timer.C:
+		case <-bfs.ctx.Done():
+			return bfs.ctx.Err()
+		}
+		backoff *= time.Duration(backoffFactor)
+		if backoff > maxBackoff {
+			backoff = maxBackoff
+		}
+	}
+	return err
+}
+
 func (bfs *Service) objectGet(ctx context.Context, oid string) (io.ReadCloser, error) {
 	u, err := url.Parse(fmt.Sprintf("neofs:%s/%s", bfs.cfg.ContainerID, oid))
 	if err != nil {
 		return nil, err
 	}
-	rc, err := neofs.GetWithClient(ctx, bfs.pool, bfs.account.PrivateKey(), u, false)
-	if err != nil {
-		return nil, err
-	}
-
-	return rc, nil
+	var rc io.ReadCloser
+	err = bfs.retry(func() error {
+		rc, err = neofs.GetWithClient(ctx, bfs.pool, bfs.account.PrivateKey(), u, false)
+		return err
+	})
+	return rc, err
 }
 
 func (bfs *Service) objectSearch(ctx context.Context, prm client.PrmObjectSearch) ([]oid.ID, error) {
-	return neofs.ObjectSearch(ctx, bfs.pool, bfs.account.PrivateKey(), bfs.cfg.ContainerID, prm)
+	var (
+		oids []oid.ID
+		err  error
+	)
+	err = bfs.retry(func() error {
+		oids, err = neofs.ObjectSearch(ctx, bfs.pool, bfs.account.PrivateKey(), bfs.cfg.ContainerID, prm)
+		return err
+	})
+	return oids, err
 }
 
 // isContextCanceledErr returns whether error is a wrapped [context.Canceled].